Prior forced air deicing systems inject the glycol in an air stream air causing the glycol to atomized and dispersed in the air. Such streams lack the cleaning capacity to dislodge and remove ice from aircraft wings.
Conventional aircraft deicing systems consist of ground or truck mounted spray systems which apply hot (180.degree. F.) deicing fluid (a mixture of glycol and water) at rates up to 60 gpm to the aircraft surfaces. This thermal process is very effective in quickly melting the snow or ice from these surfaces, i.e. wings, etc. However, glycol is expensive and toxic creating significant economic and waste management problems for airline and airport operators. The life cycle cost of deicing glycol (i.e. Type I ethylene or propylene glycol) includes costs associated with its buying, storing, handling, heating, applying, collecting and reprocessing or disposal. Various deicing systems using little or no glycol have been tried and to date these systems have demonstrated limited effectiveness. Therefore, they have not gained acceptance by commercial deicing operators.
Ground deicing of aircraft is an important step in preparing aircraft for safe flight during snow, ice and frost weather conditions. Accumulation of these winter products on aircraft surfaces (wings, tail and rudder) disturbs the aerodynamic performance of these surfaces creating unstable flight conditions. While conventional hot deicing fluid washdown of aircraft is very effective in removing these accumulations, glycol is expensive and toxic. Furthermore, the deicing process takes time which causes flight delays during the winter months. This combination of cost, waste management and flight delays creates a significant economic burden for the airlines during winter operations. Therefore, a deicing process that is efficient, i.e. sharply reduces glycol usage and deicing cycle time, is in high demand by the airline industry.
Conventional aircraft deicing by hot deicing fluid (Type I) washdown from ground or mobile boom systems has been in use for decades with no basic changes to this technology other than refinements to the deicing fluid heating and application systems. Some of the patents covering conventional deicing and its refinements are as follows U.S. Pat. No. 3,243,123, to D. M. Ingraham, et. al., issued Mar. 29, 1966, U.S. Pat. No. 4,073,437 to Thornton-Trump, issued Feb. 14, 1978; U.S. Pat. No. 4,826,107 to Thornton-Trump, issued May 2, 1989 and U.S. Pat. No. 5,028,017, to Simmons, et al., issued Jul. 2, 1991. Other publications describe various deicing systems, (some of which are believed to have been tested) to improve the deicing process, either by reducing or eliminating the use of glycol, or by applying glycol in a more efficient manner such that the glycol usage is reduced for instance: U.S. Pat. No. 5,244,168 to Williams, issued Sep. 14, 1993 for A Methodology And Apparatus For Forced Air Aircraft Deicing and U.S. Pat. No. 5,104,068 to Krilla et al., issued Apr. 14, 1992.
Forced air deicing ("hot air blasts") has been used by the U.S. Air Force for decades. At Air Force bases such as Elmendorf AFB in Alaska, operators use deicing trucks that have an add-on forced air system. Landoll is one company that modifies deicer trucks with forced air add-on for Air Force use. These Landoll add-on systems, use air from a Garrett (now AlliedSignal) APU that is plumbed to a second (non gylcol carrying) nozzle located along with the conventional deicing fluid nozzle(s) at a boom basket. Forced air is used to remove much of the snow from military aircraft followed by conventional fluid deicing. This process, which extends deicing cycle time, is viable for the Air Force because they are typically not constrained by strict time schedules, like commercial airlines, and glycol usage is reduced.
Deicing fluid entrained in air has been know for a number of years, see for instance U.S. Pat. No. 2,482,720 Prevention of Ice Formation in Air Intakes on Aircraft and Other Fast Moving Vehicles, (1949) and Palmatier, "Fan Deicing or Anti-Icing Means", U.S. Pat. No. 2,406,473 (1946).
Referring now to FIG. 1, that shows an illustration of prior art forced air deicing system of the type disclosed in U.S. Pat. No. 5,244,168, that injects glycol A at right angles to the primary flow axis of an airstream B, generally producing what is described in that patent as "a well-dispersed atomized spray pattern" (col 7 line 35) or a "spray pattern of a high speed colloidal suspension of deicing fluid in air" (claim 1, lines 21-22). This patent also requires the uses of a "plurality of sources of deicing fluid." (see col 2, line 34 col line 32).
Various airline operators have indicated that glycol injected at a right angle to the primary axis of the airstream, as is shown in FIG. 1, reduces the effectiveness of forced air deicing. The glycol mixes and atomizes in the airstream. The energy transfer process associated with the mixing and atomizing reduces the kinetic energy of the airstream which reduces the effectiveness of the air stream/glycol mixture to dislodge snow and ice that is frozen to or adhered to an aircraft. Thus, this atomization process reduces the effectiveness of the airstream in breaking loose snow and ice that is frozen to or adhered to an aircraft surface and also reduces the effectiveness of the airstream in moving heavy, wet snow. In addition, the mixture of atomized glycol and high velocity air adds more wetness to the snow further inhibiting the removal of wet snow.
Another novel deicing technique developed by InfraTek Radiant Energy Corporation uses gas-fired infra-red heaters built into the interior structure of a large prefab type hangar to melt ice from the aircraft surfaces. Two fundamental problems have surfaced with this deicing process. First, the frequency of the infra red heaters is such that snow melts slowly extending the deicing cycle time. Second, testing to date shows that melting ice from the upper surfaces of the aircraft often re-freezes on the lower surfaces not exposed to the infra-red rays.
U.S. Pat. No. 5,104,068 Krilla et al. for a "Apparatus and Method for De-Icing and Anti-Icing (and/or Cleaning and Rising Aircraft)" describes an apparatus for both de-icing and anti-icing an aircraft in one "pass". The apparatus consists of articulated booms on each side of the aircraft to be processed. These booms are such that they extend over the entire length of each wing and each has two series of nozzles. One set is for dispensing a deicing fluid mixture and the other set of nozzles dispenses anti-icing fluid. There is also a set of booms underneath the aircraft for processing the lower aircraft surfaces. The patent also describes the use of different mixtures of pressurized air, water and glycol (Type I) with the mixture varied in accordance with the particular weather conditions. The apparatus and process described above are commercially known by the name "Whisper Wash" expected to be field demonstrated during the winter of 1996-7. Benefits expected to be realized presumably include, reduced glycol usage and reduced de-ice/anti-ice cycle time.